Mobile Computing Middleware - A Peek into Jini, UPnP and OSGI Saad Liaquat Kiani RTMM Lab Saad Liaquat Kiani

Mobile Computing Mobile, computing means that the computing device is not continuously connected to the base or central network. Mobile devices include PDAs, laptop computers, and many of today’s cell phones (aptly called "smart phones"). These products may communicate with a base location with or without a wireless connection. An example of a wireless mobile application is using a modem-equipped PDA to receive text messages via satellite technology. Saad Liaquat Kiani

Types of Mobile Devices A categorization of five different types of mobile devices: Laptop computers PDAs and handheld PCs Pagers Smart phones and cellular phones Task devices, such as bar code scanners Laptops are typically used and supported in the same way as desktop PCs. Many organizations have replaced desktops with their portable cousins as the workforce has grown increasingly mobile. PDAs are the least planned-for and supported devices. They are undergoing rapid evolution and are being brought into organizations in the same way the earliest PCs were. Smart phones that allow users to access phone calls, two-way radio transmissions paging and data transmissions Task devices such as the parcel tracking devices used by Federal Express (FedEx) and the United Parcel Service (UPS) Saad Liaquat Kiani

Types of Mobile users Three types of mobile users: Telecommuters who work away from the office but connect directly to the office from a remote location. Casual telecommuters and other workers who work a few days per month outside the office. Predominantly mobile employees Percentage of Workforce Mobility Saad Liaquat Kiani

Distributed Middleware Middleware is an enabling layer of software that resides between the application program and the networked layer of heterogeneous platforms and protocols. It decouples applications from any dependencies on the plumbing layer that consists of heterogeneous operating systems, hardware platforms and communication protocols Most distributed applications and services were designed with the assumption that the terminals were powerful, stationary and connected to fixed networks. Conventional middleware technologies thus have focused on masking out the problems of heterogeneity and distribution to facilitate the development of distributed systems. They allow the application developers to focus on application functionality rather than on dealing explicitly with distribution issues. Different middleware systems such as CORBA, DCOM and Java RMI have proved their suitability for standard client-server applications. However, under the highly variable computing environment conditions that characterize mobile platforms, it is believed that existing traditional middleware systems are not capable of providing adequate support for the mobile wireless computing environment. There is a great demand for designing modern middleware systems that can support new requirements imposed by mobility. Saad Liaquat Kiani

Why separate middleware for mobile computing ? There are at least three common factors that affect the design of the middleware infrastructure required for mobile computing: mobile devices network connection mobility Mobile devices vary from one to another in term of resource availability Devices like laptops can offer fast CPUs and large amount of RAM and disk space while others like pocket PCs and phones usually have scarce resources. It is either impossible or too expensive to augment the resource availability Hence, middleware should be designed to achieve optimal resource utilization. Network connection in mobile scenarios is characterized by limited bandwidth high error rate higher cost frequent disconnections due to power limitations available spectrum Mobility Saad Liaquat Kiani

Why separate middleware for mobile computing ? Physical host mobility can greatly affect network connection Mobile clients may interact with different types of networks, services, and security policies as they move from one area to another. This requires applications to behave differently to cope with dynamic changes of the environment parameters. Due to these limitations, conventional middleware technologies designed for fixed distributed systems are not prepared to support mobile systems. They target a static execution platform where the host location is fixed, the network bandwidth does not fluctuate, and services are well defined Saad Liaquat Kiani

Mobile Computing: Reference Technologies The remaining of the presentation will briefly describe 3 middleware technologies that can aid mobile devices in utilizing existing network infrastructure and resources UPnP Jini (Java RMI) OSGI Saad Liaquat Kiani

Universal Plug and Play Universal Plug and Play (UPnP) is a standard software architecture for peer-to-peer network connectivity of intelligent appliances, wireless devices, and PCs. A device can dynamically join a network obtain an IP address convey its capabilities discover other devices learn the capabilities of other devices. A UPnP enabled device can control remote devices, and transfer data to and from remote devices. Devices can subscribe to events that may occur as state variables change. Subscription to events allows a distributed device to react to remote events e.g., when a track stops playing, start playing the next track. A device can leave a network smoothly and automatically without leaving any unwanted state behind. Saad Liaquat Kiani

UPnP UPnP leverages Internet technologies Internet Protocol (IP) [TCP, UDP] HTTP XML. Like the Internet, UPnP is based on wire protocols that are expressed in XML, and communicated via HTTP IP internetworking is a strong choice for UPnP because its proven ability to span different physical media to enable real world multiple-vendor interoperation to achieve synergy with the Internet and many home and office intranets. Saad Liaquat Kiani

UPnP UPnP devices can be implemented using any programming language, and on any operating system. UPnP does not specify or constrain the design of an API for applications running on control points; OS vendors may create APIs that suit their customers' needs. Saad Liaquat Kiani

UPnP Coordination in a NutShell Announcing presence Use SSDP and Directory service proxies (optional) Discovering other devices Listen to SSDP multicast channel directly or contact a directory service proxy. Describing capabilities XML description of the device is made available at a specified URL Self configuration This is primarily DHCP or AutoIP, and multicast DNS. Auto configuration seems to be the strongest feature of UPnP as yet. Invoking Services Transports: TCP/IP and proxies to other transports Saad Liaquat Kiani

UPnP Example You wake at 6 a.m. to a view of the mountains and a current ski report: snow is falling and the powder is piling up. You send an alert via your alarm clock to your children's alarm clocks and the coffeepot. The coffee starts brewing, you hear the patter of steps upstairs as the kids get out of bed, and soon you're all off to an early start to the mountains for a day of skiing. Saad Liaquat Kiani

Jini Motivation Enable devices / services enter and leave the network without requiring explicit reconfiguration Jini is a Java based distributed computing environment, that offers “network plug and play” Allows devices to dynamically establish communication to share and exchange services across a network Simplifies interactions with a network and connections between devices anytime anywhere. Enables devices to plug together to form an impromptu community-a community put together without any planning, installation or human intervention. Saad Liaquat Kiani

Jini operations Lookup service  The Service Registry supports searching for services that meet certain criteria, e.g. those that have a particular Java type Services  Devices or Software Service Object  Contains the Java programming language interface for the service. Contains methods that users and clients will invoke to execute the service A Device hosting a service registers with the Lookup service to announce its presence A Client wishing to use a particular service, asks the Lookup service for contact information about the service to be used The process of finding a Lookup service, either by client or device/service is called Discovery The process of registering a device/service with a Lookup service is called Join The process by which a client finds a service/device of interest from a Lookup services is called Lookup The process of using a service by the client is called Service Invocation Service Provider register Service Registry (Lookup Service) lookup Service User Saad Liaquat Kiani

Jini Architecture Jini Java Spaces Other Services ••• Lookup Network Services Java Spaces Other Services ••• Lookup Jini Discovery/Join RMI Java Java Java Solaris Mac Windows x86 Saad Liaquat Kiani

Jini Benefits Self Healing Networks through Leasing Distributed Events Leasing provides a method of managing resources in an environment where network failures can occur A service is only provided for a certain amount of time unless the provider re-registers it (renews the lease) Similarly, resource is not granted to a consumer for indefinite period, but “leased” for a finite time Keeps dead services from accumulating in the lookup servers over time Distributed Events Extends Java event model to allow it to work in a distributed network Register interest, receive notification Event Mailboxes (Asynchronous event mechanism) receive event notifications on behalf of their clients and deliver them later upon request supports disconnected operations, unexpected failures of modules and maintaining history of events of interest Saad Liaquat Kiani

OSGI The OSGi™ specifications define a standardized , component oriented , computing environment for networked services . Adding an OSGi Service Platform to a networked device (embedded as well as servers), adds the capability to manage the life cycle of the software components in the device from anywhere in the network. Software components can be installed, updated, or removed on the fly without having to disrupt the operation of the device. Software components are libraries or applications that can dynamically discover and use other components. Software components can be bought off the shelf or are developed in house. The OSGi Alliance has developed many standard component interfaces that are available from common functions like HTTP servers Configuration Logging Security user administration XML Plug compatible implementations of these components can be obtained from different vendors with different optimizations. Software component architectures address an increasing problem in software development: The large number of configurations that need to be developed and maintained. The standardized OSGi component architecture simplifies this configuration process significantly. Saad Liaquat Kiani

OSGI Framework The OSGI Framework provides a standardized environment to applications (called bundles). The Framework is divided in a number of layers. L0: Execution Environment L1: Modules L2: Life Cycle Management L3: Service Registry The L0 Execution environment is the specification of the Java environment. Java 2 Profiles, like J2SE, CDC,, MIDP etc. are all valid execution environments.  The L1: Modules layer defines the class loading policies. The OSGi Framework is a powerful and rigidly specified class loading model. It is based on top of Java but adds modularization. The L2: Life Cycle layer adds bundles that can be dynamically installed, started, stopped, updated and uninstalled. The L3 layer adds a Service Registry. The service registry provides a comprehensive model to share objects between bundles. A number of events are defined to handle the coming and going of services Many services are server like objects, like an HTTP server, other services represent an object in the real world, for example a Bluetooth phone that is nearby Saad Liaquat Kiani

OSGi The OSGi specifications are so widely applicable because it is a small layer that allows multiple, Java™ based, components to efficiently cooperate in a single Java Virtual Machine (JVM). The presence of OSGi based middleware in many different industries is creating a large software market for OSGi software components. The rigid definition of the OSGi Service Platform enables components that can run on a variety of devices, from very small to very big. Saad Liaquat Kiani

Protocol Services The OSGi Alliance has defined a number of services that map an external protocol to an OSGi service. Http Service – The Http Service is, among other things, a servlet runner. Bundles can provide servlets, which becomes available over the Http protocol. The dynamic update facility of the OSGi Service Platform makes the Http Service a very attractive web server that can be updated with new servlets, remotely if necessary, without requiring a restart. UPnP Service – Universal Plug and Play (UPnP) is an emerging standard for consumer electronics. The OSGi UPnP Service maps devices on a UPnP network to the Service Registry. Alternatively, it can map OSGi services to the UPnP network. This is a recommended Release 3 specification. Jini Service – Jini is a network protocol used to discover Jini services on a network and download those services in the host as Java code and execute them. This is recommended Release 3 specification. Saad Liaquat Kiani

References UPnP Jini OSGI http://www.upnp.org http://www.artima.com/jini http://www.jini.org http://www.sun.com/software/jini/ OSGI http://www.osgi.org Saad Liaquat Kiani